The present invention relates to an expandable honeycomb structure such as used for window coverings. The structure is made of foldable material which in the expanded condition defines a plurality of longitudinally extending cells, one on top of the other. In the retracted or collapsed state of the honeycomb structure, the adjacent cells are collapsed on each other.
The prior art discloses various honeycomb structures made from foldable material. Representative of such prior art are the Rasmussen Pat. Nos. Re. 30,254, and Re. 31,129, the patents to Suominen, U.S. Pat. Nos. 4,288,485 and 4,388,354, and the patent to Masuda, U.S. Pat. No. 3,164,507. In addition, U.S. Pat. No. 4,450,027 to Colson discloses a honeycomb structure constructed from foldable material which is folded longitudinally of the material and wound onto a rack in overlying layers. The layers are adhered together to form the cells of the honeycomb structure. The present invention is most directly a variation of the honeycomb structure and method of making it as disclosed in the '027 patent.
In making window blinds or panels out of the honeycomb structures of the prior art, it is sometimes desirable, either for aesthetic or mechanical reasons, to have the opposite sides of the blind of different physical characteristics. For example, where thermal insulation against heat or cold is desired, the outside of the blind may be constructed to provide a heat reflective or absorbent surface whereas the inside a more decorative surface. Also, where pure aesthetics are concerned, opposite sides of the blind may simply be of different colors. Colors may also be used for providing thermal characteristics to the blind in addition to the insulation characteristic provided by the basic honeycomb structure described in the '027 patent.
With the prior art honeycomb structures, providing different physical characteristics on the opposite sides of the structure requires the use of different materials for the opposite sides which must be separately adhered together. Alternatively, where the honeycomb structure is made of a single piece of material as in the '027 patent, the different portions which will define the opposite sides of the structure have to be separately processed prior to the formation of the honeycomb configuration. In the latter type of construction, problems of alignment of the treating process can occur. For example, where different parts of the material must be treated differently across the width of the material, the line of demarcation between the two different surfaces must be fairly accurately formed. This is necessary so that the line will be hidden in the final structure. Otherwise, the physical characteristics meant for one side of the final honeycomb structure may show through on the other side in the expanded condition of the cells.
Another aspect of the honeycomb structures of the prior art relates to the creasing or pleating of the material forming each cell along fold lines. One reason pleating is provided is to assist in the orderly collapsing of the individual cells as the structure is moved from an expanded to a retracted position. Without pleats, the collapsing of the cells would tend to be haphazard and not give a neat appearance to the structure.
There are generally two types of honeycomb cell constructions. One is where the pleats generally hang out in the expanded condition of the honeycomb structure. That is, the opposite sides of the honeycomb structure generally lie in parallel planes with the connection of the adjacent cells extending completely across each cell from one side of the structure to the other. Another type of cell construction is disclosed in the '027 patent. Here, the pleats are formed to be permanent and they do not hang out in the expanded condition of the structure. With this construction, the adjacent cells are joined together over a distance which is less than the spacing between the opposite sides of the honeycomb structure.
If the pleats in the type of honeycomb structure disclosed in the '027 patent are not carefully and properly formed, they will tend to hang out. This is especially so after long, continued use of the structure with the expanded condition being one where the cells lie one on top of the other. In such an orientation, the weight of the structure itself pulls on the material of the overlying cells with the greatest forces being exerted at the top of the structure by the entire weight of the underlying cells. Any falling out of the pleats tends to increase the overall height of the structure over the height as initially manufactured. The effect of this can be unpleasing and unsatisfactory, both aesthetically and physically.